Multilayer coil components suitable for reduction in size have been widely used in recent years. These components have a structure formed by stacking a plurality of conductor patterns for a coil and a plurality of magnetic layers with a coil conductor provided in the laminate.
Among these multilayer coil components, closed magnetic circuit multilayer coil components have a problem that when a superimposed direct current is gradually increased, the inductance is substantially constant or gently decreased up to a certain current value, while beyond the current value, magnetic saturation is caused to rapidly decrease the inductance.
Thus, in order to remedy this problem, it has been known that multilayer coil components are made to have an open magnetic circuit by inserting a nonmagnetic layer near the center of a coil in the stacking direction of a laminate composed of stacked magnetic layers.
As such open magnetic circuit multilayer coil components, Japanese Patent Application Laid-Open No. 2004-311944 (Patent Document 1) proposes a multilayer coil component in which a nonmagnetic layer (an insulating layer) composed of B2O3—SiO2-based glass or Al2—O3—SiO2-based glass is inserted between magnetic layers composed of an Ni—Zn—Cu—based ferrite material.
However, the shrinking behavior during firing is different between the Ni—Zn—Cu-based ferrite material and the B2O3—SiO2-based glass or Al2O3—SiO2-based glass, leading to a problem that defects such as cracks are likely to occur.
In addition, Japanese Patent Application Laid-Open No. 2005-259774 proposes an open magnetic circuit multilayer coil component in which a nonmagnetic layer composed of a Zn—Cu-based nonmagnetic ferrite material is inserted between magnetic layers composed of an Ni—Zn—Cu-based ferrite material.
In the case of this open magnetic circuit multilayer coil component, there is no significant difference in shrinking behavior during firing between the nonmagnetic layer and the magnetic layer, thus allowing the occurrence of defects such as cracks to be suppressed. However, since the nonmagnetic layer contains no Ni, Ni is likely to be diffused from the magnetic layer to the nonmagnetic layer, leading to a problem that the temperature characteristics of inductance for the multilayer coil component is degraded due to the diffusion of Ni (the rate of inductance change with temperature is increased). In particular, when the thickness of the nonmagnetic layer is designed to be small, the open magnetic circuit multilayer coil component has a problem that the temperature characteristics of inductance are significantly degraded due to diffusion of Ni from the magnetic layer to the nonmagnetic layer. In an open magnetic circuit multilayer coil component, while it is preferable to reduce the thickness of the nonmagnetic layer as much as possible in order to increase the initial inductance, the temperature characteristics of inductance is actually significantly degraded when the thickness of the nonmagnetic layer is reduced to 40 μm or less.